Conventionally, as a technique for reducing noise in a space (noise propagation path) through which noise emitted from a noise source propagates, there is a muting device that uses active noise control. The active noise control is a technique for actively reducing noise by emitting a canceling sound with opposite phase and the same amplitude with respect to the noise.
Conventional techniques (see, for example, Patent Literatures (PTLs) 1 and 2) disclose a configuration in which a canceling sound is generated by updating filter coefficients in an adaptive digital filter by using a least mean square (LMS) algorithm. The LMS algorithm computes a filter coefficient by using an update parameter (step size parameter: a parameter that defines the magnitude of the amount of correction in every repetition).